Test Evpower cell board

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Test Evpower cell board

Postby offgridQLD » Sat Mar 12, 2016 10:34 pm

I test a cm180R v1 Designed for 180ah lifepo4 cells

It is supposed to be able to bleed up to 1000mah and start bleeding current at 3.600v. It's also supposed to trigger the one wire loop at 4.000v high voltage and 2.600v low voltage. It's listed as consuming 2.00ma at nominal voltage.

First test is to see what the cell board consumes at 3.2000v. Turns out they consume 2.02ma, spot on what the specs list :D

Image

They don't start shunting any current befor 3.6000v and current starts to bleed bang on 3.600v. Though it ramps up very slowly. By 3.6100v it has only risen to 9ma and 2ma of that is idle consumption. 7ma of bleed :|
Image


at 3.6300 we are only at 100ma and then it continues on adding roughly 50ma every 0.01v increase.Though its not completely linear.

Image

So by 3.6500 we are only bleeding 200mah. By 3.7000v we have 450mah. 3.7500v we have 650ma bleed. At 3.800v 700ma. 3.8500v 730ma.

By 4.000v we have 800mah and at this stage the one wire loop should trigger for HVD. It didn't trigger at this point.
Image

The one wire loop triggered HVD at 4.0764v and was bleeding 838ma at that stage.
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So as you can see it is impossible for the board to bleed 1000ma as HVD is triggered befor you got there at 838ma bleed at 4.0764v :roll: I would say most people wouldn't want to see higher than 3.7000V on a cell when balancing and even at that point your only bleeding around 400ma 40% of what the board is listed to be able to bleed.


Conclusion the current bleed voltage set point needs to be set way lower and we need to see the max advertised bleed current come on stronger faster. HVD is way to high for my liking though I guess as a emergency stop it's ok. I didn't see it bleed anything befor 3.6000v just its 2ma idle load so that's good. Though stage two of the test is to test LVD set point and then test consistency across all 16 cell boards.

Kurt
Offgrid 2008, Selectronic PS1 6kw/48v inverter, x 2 Midnite solar classic 150 MPPT, 3960w NE PV 24 x 165w BP panels, 4200w NW PV 21 x 200w DAQO PV, 16x400ah lithium.
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Re: Test Evpower cell board

Postby australsolarier » Sun Mar 13, 2016 9:06 am

the HVD probably has a timer on it, that is why it propably went slightly over 4V.

all voltages for 12V lifepo4 battery block:
on my gbs lifepo4 batteries it has stickers: bulk 14.4V - 14.6V, float 13.6V - 13.8V
those settings would fit in with the bms/bcu.

however then in one of the manuals ev power then recommends bulk 14V, float 13.4V and recommends going weekly to 14.6V for balancing. this is pretty much what we are doing. (at least kurt, gordon and i)

the reason i suspect the controll electronics is chinese, he mentions in the bcu manual that when there is cold air temperature (0 degrees) the bcu shows chinese characters.

possibly rod designed the electronics, but it would still have been made in china. on alibaba you can buy similar systems with the bcu/bms. but i have not looked into what kind of system or specs they have. at the time it was not worth the trouble for direct import. customs and taxes etc. also warranty. at least you can fall back to ev power when problems or questions come up. rod does answer them quickly and seems to be open to suggestions.

my bcu also has a SOC counter. but it is highly inaccurate if you go longer than a day. 56V absorb on the 48V battery bank resets it to 100%. the battery in and out meter is more accurate and is much better to see than the small read out on the midnite classic. so when you go into the shed you see at a glance the batV and charge/discharge current. (midnite classic could/ should manufacture a large display as an accessory....)

all in all that gbs/bms/bcu is a good package. bascially you just wire up the parts and you are ready to go.
and again THAN YOU VERY MUCH KURT for your experiments. we certainly now know more how that mysterious bms circuit board works.
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Re: Test Evpower cell board

Postby australsolarier » Sun Mar 13, 2016 9:15 am

my circuit board says CBM LFP 08 R1.00 (on both the 300a/h and 400a/h batteries)
and also that is patented
so i suppose rod did design it.
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Re: Test Evpower cell board

Postby offgridQLD » Sun Mar 13, 2016 9:27 am

The boards do what they are listed to do. It's just the current bleed is a way less than you would expect between 3.6000v and say 3.7000v. You would really need a tiny trickle of charge current 10 - 400mah to Ballance in that range. Then to balance with 600 -800mah you need to be crazy high 3.8500 - 40000v+

I assume for the 400ah boards rated at 2A you could just double the numbers for the 1A rated board. So 20ma to 800ma bleed current in the 3.6000v to3.7000v range. They would most likely max out at 1600ma at hvd.

Off topic but as for the SOC readings on a midnite charger with WBJ. I never use the LED display on the units themselves. I use there PC app inside the house or a Android app to show the data. You could project the SOC meter 10 foot wide on a projector if you wanted. Though I'm happy with a visual meter 1/2 the screen of a 7" tablet. Easy to read from the other side of the living room when it's in the kitchen.

Kurt
Offgrid 2008, Selectronic PS1 6kw/48v inverter, x 2 Midnite solar classic 150 MPPT, 3960w NE PV 24 x 165w BP panels, 4200w NW PV 21 x 200w DAQO PV, 16x400ah lithium.
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Re: Test Evpower cell board

Postby australsolarier » Sun Mar 13, 2016 9:54 am

another thing about that 3.6V starting the bms just occurred to me:
we have the total voltage of the battery and the individual cell voltages. lets say the total voltage in a 12v battery for arguments sake is 4 x 3.6v = 14.4v.
but lets say you have 3 cells at 3.5v ( 3x3.5=10.5v, 14.4 - 10.5 = 3.9v )
so in this case you have three cells at 3.5V and one at 3.9V
in this scenario the bms is hard at work at the rogue cell before the average of 3.6v
so there are many things involved, like charging currant (the lower the currant the longer it hangs in that bleeding voltage)

the above example is somewhat on the extreme side, just for the purpose pointing out my point.
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Re: Test Evpower cell board

Postby offgridQLD » Sun Mar 13, 2016 10:01 am

That's not extreem that's what happens but we dont want the cells to go above 3.6v and to Ballance the pack with the board we do.

Unless you have a very well matched bank of cells and the ability to charge at a stable very low rate you will be hitting the hvd befor the boards are able to Ballance the cells.

Thats why I don't use them I use a charger to Ballance my cells as the board are to wimpy and I want them all balance in the 3.6v range not having cells drifting up in the danger zone to get the job done.

Kurt
Offgrid 2008, Selectronic PS1 6kw/48v inverter, x 2 Midnite solar classic 150 MPPT, 3960w NE PV 24 x 165w BP panels, 4200w NW PV 21 x 200w DAQO PV, 16x400ah lithium.
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Re: Test Evpower cell board

Postby australsolarier » Sun Mar 13, 2016 10:18 am

the boards were probably designed to be active in every absorb cycle in that high voltage.

with other words we do not want to go to that high absorb every day.

i think we all agree with that.

doing the high absorb cycle once a month with the 12v lifepo4 battery seemed to be enough to keep a fairly decent balance. that battery gets discharged to 50 - 60 % SOC on a daily basis.
(that small 12v300a/h system does two thirds of the house consumption. at least 9months in the year. the larger 48v/400a/h system has yet to be connected to the house. i am waiting for the 60cents feed in tariff to end at the end of this year. it is connected to a 3 panel array and boils the kettle, washing machine, microwave. half of the charge is used for the inverter.)

listening to a lecture about lifepo4 battery technology the guy basically says, the best way is to match the batteries. basically you charge and discharge them and there are a few other parameters and then match groups that are close together.
https://www.youtube.com/watch?v=QlDd3jkcxoQ

very interesting, watched it twice.
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Re: Test Evpower cell board

Postby offgridQLD » Mon Mar 14, 2016 9:41 am

Yes, having a matched battery cells from the start is the key to not needing to much cell level interference/ balancing.

The cells in my OEM electric car all 88 of them are always within 5mv when fully charged and they stay tight all the way to the very low DOD. From what I can make of it the cells are being balanced at all times. Though the kind of lithium chemistry that is used has a much more linear charge profile so it's much easier to predict SOC and balance over the full sweep than lifepo4.

As I mentioned in Gordons 400ah lifpo4 thread I think there has been some improvement or at least a effort . Though perhaps just a marketing strategy. To improve the Constancy of the cells with the new CA range of Calbs.

I also think in a Stationary storage (offgrid house) application you really need to balance your cells at a time when there is minimal load on the cells. Or at least a very stable load. If your using the Ev power boards perhaps even to the point of picking a time once a month or two that you shut down the inverter. Just let the charge current taper down to almost nothing at your preset absorb/ or EQ (how ever you want to to do it) that way you can get a stable charge voltage below 1A. Rather than a spiky situation where your charge controller is chasing the loads and you will always get some drift up and down of a amp or two as it attempts to maintain V absorb.

If you do the balance in stages it might help some . rather than going from a low SOC and trying to hit the bank with a high absorb V in one hit. Bring the voltage up and trim the stray cells with a load or a charge at cell level. Then bring it up some more and get it to the point where the charge current to maintain that balance voltage is almost nothing. Again this is easy to do in a electric car or a battery on a mains charger without loads . Harder in a live offgrid system.



Kurt
Offgrid 2008, Selectronic PS1 6kw/48v inverter, x 2 Midnite solar classic 150 MPPT, 3960w NE PV 24 x 165w BP panels, 4200w NW PV 21 x 200w DAQO PV, 16x400ah lithium.
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Re: Test Evpower cell board

Postby offgridQLD » Mon Mar 14, 2016 10:28 am

On Sunday I tested the LVD on the boards and it triggered around 2.5400V. Next test this weekend will be to test the other 15 boards to see if they bleed current in the same in the 3.6 - 3.75v range as I have this documented in 0.01v increments across this range. Its a little tedious but worth checking I think.

Kurt
Offgrid 2008, Selectronic PS1 6kw/48v inverter, x 2 Midnite solar classic 150 MPPT, 3960w NE PV 24 x 165w BP panels, 4200w NW PV 21 x 200w DAQO PV, 16x400ah lithium.
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Re: Test Evpower cell board

Postby APR » Tue Mar 15, 2016 11:06 am

This is interesting stuff Kurt. I am keen to see how consistent you find the balancers to be.

Good work and appreciated.
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